Homework Help:
Which is an example of the electromagnetic force?

This was a question on an online homework for a modern physics class. I had two chances to answer it, but I was wrong both times, so I'm simply curious what the answer is.

1. The problem statement, all variables and given/known data

Which of the following statements shows the electromagnetic force at work?

(a) Quarks attracted to one another within a proton
(b) A stable nucleus of 4 protons and 5 neutrons
(c) Collapse of a star into a black hole
(d) Beta decay of 139Ba
(e) A rubber band stretching but not breaking

3. The attempt at a solution

(a) Quarks attracted to one another is the strong force
(b) A stable nucleus of 4 protons (Beryllium) and 5 neutrons is the strong force
(c) Collapse of a star into a black hole is gravitational force
(d) Beta decay of 139 Ba is the weak force
(e) A rubber band stretching but not breaking... must the the electromagnetic force?

'e' is the correct answer. while 'b' and 'd' are both nuclear forces. I'm not sure what might be tripping you up, but one thing to consider is that in most of these situations, numerous forces are at play---but the most important one is the one listed.

Another thing to keep in mind is that all day-to-day materials (rubber bands, rocks, water, etc) are all held together by electromagnetic forces. Electromagnetic forces are the only ones involved in standard chemistry and chemical compounds.